#include <bits/stdc++.h>
#include <string.h>
#define rep(i,n) for(int i = 0; i < n; i++)
#define srep(i,a,b) for(int i = a; i < b; i++)
#define all(A) (A).begin(),A.end()
#define MOD 1000000007
using namespace std;
using ll = long long;
using P = pair<int,int>;
using Graph = vector<vector<int>>;

int main(void){
	string s; cin >> s;
	int a = 0;
	rep(i,(int)s.size()) if(s[i] == 'a') a++;
	string t = "";
	rep(i,a+1) t += "a";
	cout << t;
}